Low temperature molding process for making solid biodegradable articles

ABSTRACT

The present invention is directed toward a process for making solid biodegradable articles from wheat gluten. Hydrated wheat gluten is provided in the form of a cohesive, elastic dough. The cohesive, elastic dough comprises at least 8% by weight wheat gluten and wherein the wheat gluten comprises a protein having a primary structure. The cohesive, elastic dough is formed into a shaped article and placed in an environment sufficient to remove excess water from the shaped article without modifying the primary structure of the wheat gluten protein, such that a solid biodegradable article results. The solid biodegradable articles of the present invention comprise at least 8% by weight wheat gluten.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/599,215, entitled, “Low-Temperature MoldingProcess and Biodegradable Articles Prepared Therefrom,” filed Aug. 5,2004, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a low temperature molding process. Inparticular, it relates to a low temperature molding process that is usedto prepare solid biodegradable articles from wheat gluten.

BACKGROUND OF THE INVENTION

Waste disposal is a major global problem in the world today. Theescalating population, coupled with the use of more polymeric materials,has resulted in the creation of large landfills that are filled withnon-biodegradable materials. Efforts have been made to try to createmore biodegradable materials. These efforts are primarily focused onpreparing polymers that degrade when exposed to sunlight or tomanufacture materials from starch and other plant proteins that willdegrade in a relative short period of time under normal environmental orcomposting conditions of temperature, humidity, and the action ofmicroorganisms.

Bassi et al. (U.S. Pat. No. 5,665,152) propose a method of formingsolid, non-edible biodegradable, grain protein-based articles. A grainprotein formulation is heated to a maximum temperature of up to about80° C. to create a substantially homogeneous and flowable mixture whichcan be formed into solid biodegradable articles. The formulationincludes from about 20-85% by weight of grain protein, from about 5-75%by weight starch, up to about 14% by weight water, from about 10-40% byweight plasticizer, and at least about 0.01 by weight of a reducingagent such as sodium bisulfite for cleaving disulfide bonds present inthe grain protein. Optional ingredients such as fillers, fiber,lubricant/mold release agents and colorants can also be used. Theformulations are heated under moderate temperature conditions, usuallywith shear, to create a substantially homogeneous and flowableformulation. Thus, in the context of injection molding, the preferredtemperature conditions of molding assure essentially complete proteindenaturation. Reducing agents are an important component of theformulations because they drastically improve the flow and mixing of thegrain protein and also serve to enhance the final products in terms ofappearance, mechanical properties and moisture resistance.

Rayas et al. (U.S. Pat. No. 6,045,868) describe a method wherein grainflour proteins are crosslinked with aldehydes and bleached with ableaching agent to form crosslinked transparent polymers used as filmsfor packaging. The process uses ethanol and water for the extraction atacidic or basic pH's and optionally heating with or without a reducingagent to provide the polymer to be bleached and crosslinked. Morespecifically, the method involves the separation of biopolymericmaterials from grain flours to make plastic films by a solubilizationprocess with selected solvents. Once separated, the grain flourbiopolymers are crosslinked and plasticized to form a film-formingsolution. A heating process is preferred in order to concentrate thefilm-forming solution and denature the flour protein prior tocrosslinking and bleaching so that more protein interactions occur whenthe film is dried and stronger films are formed. The heating processmust be in the range of 30° C. up to the boiling point of the solution,with a preferred range of 60° C., up to the boiling point.

Woerdeman et al. (WO 2004/029135 A2) describe a gluten polymer matrix,with tunable material properties, produced by using polythiol-containingmolecules during the preparation process. The process for preparing thegluten polymer matrix comprises dispersing or mixing gluten in thepresence of polythiol-containing molecules or combining gluten withpolythiol-containing molecules in a gluten-dispersing mixture. Inanother embodiment of the invention, the process also comprises anisolation step which consists of precipitating the proteins or afraction thereof, for example by changing the pH of the dispersion, bychanging the concentration of one of the solvents used or by changingthe ionic strength of the mixture. When compression-molding isperformed, a minimum temperature of 100° C. and a minimum pressure of 2bars for a minimum of 1 minute is required.

Aung (U.S. Pat. No. 5,279,658) describes a composition suitable forforming into shaped articles comprising flour, starch, and water. Theflour, starch and water are each present in an amount such that thecomposition is rigid and stable over a predetermined temperature range.The composition preferably contains 40-80% by weight flour, 20-60%starch and 15-25% water. The flour and starch are obtained from naturalcereal sources, such as corn, rice, potato, tapioca and wheat. Thecomposition may be in pellet form or any other form suitable foremploying in a process for preparing shaped articles. A mixture of flourand starch are prepared wherein the flour and starch have a uniformparticle size. The mixture is heated and mixed under a sufficientpressure temperature and moisture content and for a sufficient period oftime such that when the pressure is decreased the mixture expands toform a composition which when cooled is rigid and stable over apredetermined temperature. In the cooking phase, the sifted mixture,water and any coloring and flavoring agents are fed into an extrusioncooker at a feed rate of 2-7 Kg/hour and a nozzle ratio of 2:4 with asingle or twin screw rotating at a speed of 90-220 rpm. The dough ismixed, kneaded and cooked with a moisture content of 15-35% at atemperature of 120°-200° C. and pressure of 200-300 psi. The pressure isreduced by venting resulting in expansion of the dough. The expanded hotdough is pressure injected into a form press which has a water-cooleddie mold. The expanded hot dough fast cools in the form press at thesurface of the cold die mold. The expanded packaging material is stampedto the correct thickness in the form press. The formed packagingmaterial may then be coated with a water repellant material, dried in anoven and cooled in a cooling chamber.

An object of the present invention is to provide a low temperaturemolding process for preparing solid biodegradable articles from wheatgluten.

Another object of the present invention is to provide a low temperaturemolding process that involves drying but not cooking of the wheatgluten, such that the primary structure of the wheat gluten proteinremains essentially unchanged.

SUMMARY OF THE INVENTION

In general, the present invention is directed toward a process formaking solid biodegradable articles from wheat gluten. Hydrated wheatgluten is provided in the form of a cohesive, elastic dough. Thecohesive, elastic dough comprises at least 8% by weight wheat gluten.The cohesive, elastic dough is formed into a shaped article and placedin an environment sufficient to remove excess water from the shapeddough without altering the primary structure of the wheat glutenprotein, wherein a solid biodegradable article comprising at least 8% byweight wheat gluten results. Examples of the solid biodegradablearticles of the present invention include items such as: food storagecontainers; food utensils; beverage containers; boxes; toys; biologicaldressings; medical implants; filters; and biodegradable insulation whereeach solid biodegradable article comprises at least 8% by weight wheatgluten.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part, will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention will be obtained by means ofinstrumentalities in combinations particularly pointed out in theappended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

By the present invention, a low temperature process for making solidbiodegradable articles from wheat gluten is presented. In principle,shaped articles are subjected to an environment sufficient to removeexcess water such that they are dried into solid biodegradable articles.It is desirable to have some water remain in the shaped article to actas a plasticizer. Therefore, a balance is struck between the drying ofthe outer portion of the shaped article and diffusion of water from theinside of the shaped article. This balance is achieved by employing lowtemperatures, controlling the humidity in the environment, or both lowtemperature and low humidity conditions. By low temperature, it is meantthat any heat applied above room temperature (up to a temperature lessthan about 60° C.) is applied for the purpose of driving off excessmoisture and not to alter the primary structure of the wheat glutenprotein. In particular, it is undesirable to have the wheat glutenactually cook (as evidenced by inflation of the wheat gluten) or besubject to degradation by heat. Rather, the objective is to provide anenvironment conducive to drying the shaped article. Hence, an articlehaving a soft interior is not suitable or desirable for the solidbiodegradable articles prepared by the process of the present invention.However, some superficial damage to the surface of the article as aresult of using low heat during drying is permissible, and one ofordinary skill in the art would realize that.

The process begins by providing hydrated wheat gluten in the form of acohesive, elastic dough wherein the cohesive, elastic dough comprises atleast 8% by weight wheat gluten and wherein the wheat gluten comprises aprotein having a primary structure. The wheat gluten used for thepresent invention is any form of wheat gluten known to one of ordinaryskill in the art. Preferably, the wheat gluten comprises at least 10%wheat gluten. More specifically, the wheat gluten comprises about 75% byweight wheat protein, about 10% by weight starch, about 10% by weightmoisture, about 5% by weight lipids, and about less than 1% by weightminerals. Such wheat gluten is in the form of a powder and iscommercially available and known as Amylum 110 available from Aalst inBelgium or Vital Wheat Gluten available from MGP Ingredients,Incorporated in Atchison, Kans. Alternatively, commercial wheat glutenpurified by protein fractionation or extraction is also suitable foruse.

When wheat gluten is provided in the form of a powder, any aqueoussolvent known to one of ordinary skill in the art may be employed in thepresent invention as a hydrating agent for the wheat gluten powder.Hence, the hydrating agent is not restricted to water alone but mayinclude various aqueous solvents. Examples of such aqueous solventsinclude but are not limited to: water; a dilute HCl; a dilute aceticacid; a dilute lactic acid; an aqueous NaOH; aqueous alcohol solutions;urea solutions; chaotropic agents; detergents; salt solutions; andorganic solvents capable of swelling protein chains. Preferably, theaqueous solvent is water. The aqueous-based solvent is selected based onthe mixing conditions. For example, it may be necessary to decrease thepH to 4 or lower. In such cases, dilute HCl, dilute acetic acid, orlactic acid may be used. Under alkaline conditions, aqueous NaOH may bethe solvent of choice. If strong alkaline or acidic conditions exist,the protein structure may be adversely affected. Examples of aqueousalcohol solutions include but are not limited to: alcohol/watermixtures, such as a 70% ethanol or a 50% propanol mixture. Ureasolutions are employed when it is desirable to break-up hydrogenbonding. An example of a chaotropic agent is guanidium hydrochloride.Detergents such as sodium dodecyl sulfate, cetyl trimethyl ammoniumbromide may also serve as aqueous solvents. Salt solutions are alsosuitable for this application. Other organic solvents may be used aswell, such as ketones, amide solvents, m-cresol, andhexafluoro-isopropanol, provided such solvents are capable of swellingprotein chains. Enough of the aqueous solvent must be mixed with thegluten powder to hydrate the powder and form a cohesive, elastic dough.Generally, about 0.1 to about 0.9 parts by weight of an aqueous solventis added to the gluten powder. More preferably, about 0.5 parts byweight to about 0.75 parts by weight of an aqueous solvent is added tothe gluten powder. Any of the solvents may be used in combination with areducing agent and/or oxidizing agent (such as KIO₃) to aid inoptimization of dough properties.

Additional additives are added to the formulation to achieve the desiredproperties of the article. For example, a filler is added to thehydrated wheat gluten. Any filler known to one of ordinary skill in theart may be employed, and preferably, the filler is selected from thegroup consisting of: inorganic fillers; organic fillers; reinforcementfillers; and natural fillers. Alternatively, the filler is a naturalfiller such as the shell from a shellfish and, more specifically,pulverized crustacean shells.

Processing additives are also added when desired. In particular,processing additives such as: bleachers; crosslinkers; and plasticizersare added. Specific examples of bleachers include but are not limitedto: hydrogen peroxide; ozone; calcium carbonate; and barium peroxide.Crosslinkers include but are not limited to: difunctional aldehyde;p,p′-difluoro-m,m′-di-nitrodiphenylsulfone;1,5-difluoro-2,4-dinitrobenzene; 1-fluoro-2-nitro-4-azidobenzene;phenol-2,4-disulfonyl chloride; α-naphthol-2,4-disulfonyl chloride;adipate bis-(p-nitrophenyl) ester; carbonyl bis (methioninep-nitrophenyl) ester; tartaryl diazide; tartly bis-(glycylazide);succinate bis-(hydroxyl-succinimide ester); N-(azidonitrophenyl)γ-aminobutyrate hydroxyl-succinimide ester; 1,3-dibromoacetone;p-azidophenacyl bromide; 1,1-bis-(diazo acetyl)-2-phenylethane;1-diazoacetyl-1-bromo-2-phenylethane; bis-diazo-benzidine;glutaraldehyde; polymethylene(n-3-12)di-imidate; and polythiols. Morespecific examples of difunctional aldehydes include formaldehydes andglutaraldehydes. Plasticizers such as glycerol and ethylene glycol arealso added.

Preservatives are added to prevent mold growth in the product. Suchpreservatives include but are not limited to: ascorbic acid; sulfites;phenols; calcium chloride; silica gel; propionic acid; acetic acid;inorganic acid; sodium azide; and formaldehyde. In addition, for someapplications it is desirable to add a fungicide. Pigments, ultra-violetstabilizers, and antioxidants are added as necessary to meet specificproduct requirements.

In an alternative embodiment, the hydrated wheat gluten is blended witha biodegradable polymer to form a cohesive, elastic dough. Examples ofbiodegradable polymers include but are not limited to polylactic acid orpolyvinylalcohol. In forming the cohesive, elastic dough, at least 8% byweight of wheat gluten is blended with a biodegradable polymer and water(if needed). More specifically, the proportions of wheat gluten, polymerand water are adjusted to provide a cohesive, elastic dough thatcomprises at least 8% by weight of wheat gluten.

Once the cohesive, elastic dough is provided, it is formed into adesired shape. The elastic dough is formed into shaped articles by anyprocess known to those having ordinary skill in the art. For example,three-dimensionally shaped articles are formed using a die that isinterfaced with standard equipment that is used in forming processessuch as: extrusion, injection molding, compression molding, and blowmolding. Alternatively, the forming process takes place by way ofshaping. Shaping encompasses such activities as flattening or rollingthe dough and stamping the article out from the dough. A form press mayalso be used. The forming process produces a hydrated shaped articlethat must be further dried in order for the article to achieve fullstrength. The hydrated shaped articles are similar to those of clayarticles that have yet to be fired (often referred to as green ware).

Regardless of the forming process used, in all instances, once the doughis shaped, the hydrated shaped article is placed into an environmentsufficient to remove excess water from the shaped article withoutmodifying the primary structure of the wheat gluten protein. Anenvironment sufficient to remove excess water is achieved by eithercontrolling the temperature, the humidity, or both the temperature andthe humidity. A sufficient environment would permit the escape of excesswater from the interior of the shaped article before the exterior of theshaped article is completely dry. It is desirable to retain some of thewater in the interior of the article to serve as a plasticizer for thearticle. Preferably, the environment has a temperature less than about60° C. Most preferably, the environment has a temperature less thanabout 25° C. and, in particular, ranging from about 5° C. to about 20°C. In some instances, the environment may also be a forced airenvironment that aids in the drying process. Alternatively, a lowhumidity environment having a temperature less than about 60° C. is alsosuitable for the present invention. The completion of this step yields abiodegradable article comprising at least 8% by weight wheat gluten.

As further embodiments of the invention, if cracks are present at thesurface of the solid biodegradable article, water is applied to thesurface of the shaped article to initiate crack healing. The humidity iscontrolled in the environment to make it conducive to removing excesswater without modifying the primary structure of the wheat glutenprotein. Lastly, a water repellant coating is applied to thebiodegradable article when desired.

A preferred embodiment for making the solid biodegradable articles ofthe present invention involves compression molding. In this process, thecohesive, elastic dough is flattened and positioned in a male-femalemold. The flattened dough is compressed in the mold to form a shapedarticle which is placed in an environment having a temperature less thanabout 60° C., preferably less than about 25° C., and within a mostpreferable range of about 5° C. to about 20° C. Preferably, the elasticdough is compressed using a pressure ranging from about 2 bars to about25 bars.

Additionally, the male portion of the mold is removed such that thefemale portion containing the dough remains and the female portion ofthe mold is returned to the environment having a temperature less thanabout 60° C., preferably less than about 25° C., or within a mostpreferred range of about 5° C. to about 20° C. (Alternatively, thefemale portion of the mold is removed leaving the male portion of themold having the dough disposed thereon.) When the dough has taken shape,it is removed from the low temperature environment and the male portionof the mold is replaced over the dough. The female portion is thenremoved leaving the dough disposed on the male portion of the mold. Themale portion of the mold is then returned to the low temperatureenvironment until the dough has taken shape. After the male portion isremoved from the low temperature environment, the female portion of themold is place over the male portion of the mold, such that it nowcontains the dough, the male portion of the mold is removed, and thefemale portion of the mold containing the dough is returned to the lowtemperature environment. These steps are repeated until the dough is dryto touch. At that point, the male portion and the female portion of themold are removed and the shaped article (which is similar to green ware)is placed in the low temperature environment until the shaped articledoes not yield to touch.

Alternatively, prior to compressing the elastic dough, the dough isplaced in an environment having a temperature less than about 60° C.,preferably less than about 25° C., or within a most preferable range ofabout 5° C. to about 20° C., and preferably for about 1 hour when thereis no circulating air, before it is positioned in the mold. To preventcracking during the process, water is applied to the shaped article. Airis circulated in the low temperature environment to enhance drying ofthe article.

The solid biodegradable articles of the present invention are completelybiodegradable and achieve their full strength at temperatures below 60°C. In addition, when no additives are contained in the starting dough,the articles are safe for consumption. At a minimum, the solidbiodegradable articles comprise at least 8% by weight wheat gluten andthe primary structure of the wheat gluten protein has not been modified.

Example

Materials. Two sources of commercial wheat gluten were used in thisstudy: the first source was commercial wheat gluten (70.2% protein on an“as-is basis” as determined by the Dumas Method (N×5.7)) from Amylum(Aalst, Belgium), while the second source was commercial wheat gluten(75% protein (N×5.7) as reported on the supplier ‘Technical Data’ sheet)from MGP Ingredients, Inc. (Atchison, Kans., USA).

Experimental. 100 g of wheat gluten powder was combined with roughly 60g of water. Ingredients were thoroughly mixed for several minutes untilthe gluten powder was well-hydrated, and the gluten dough had attainedmaximum strength (as defined by cereal chemists.) Afterwards, the doughwas flattened, and draped over a male-egg-carton-shaped-mold. The femalecounterpart was placed over the dough and the entire assembly was thenplaced in a refrigerator under a 5 lb weight. After 8 hrs, the weightwas removed, along with the female portion of the mold. The open maleportion of the mold was returned to the refrigerator to allow the doughto dry over a period of several hours. After 8 hrs, the dough wasremoved from the male mold and repositioned in the female mold. Afteranother 8 hrs of drying time, the specimen was replaced on the malemold, to allow for uniform drying. When the specimen no longer yieldedto touch, it was removed entirely from the mold, and returned to therefrigerator to allow for further drying. When the gluten egg carton hadgained sufficient strength, it was removed from the refrigerator fortesting. The above procedure renders a bioplastic specimen free ofcracks and surface defects.

The above description is only illustrative of preferred embodimentswhich achieve the objects, features and advantages of the presentinvention, and it is not intended that the present invention be limitedthereto. Any modification of the present invention which comes withinthe spirit and scope of the following claims is considered part of thepresent invention.

1. A solid biodegradable article selected from the group consisting offood storage containers, food utensils, beverage containers, boxes, toysand filters prepared by forming a cohesive, elastic dough consistingessentially of hydrated wheat gluten prepared by mixing at a temperatureless than about 60° C. from about 0.1 to about 0.9 parts by weight of acommercial wheat gluten purified by protein fractionation or extractionwith from about 0.9 to about 0.1 parts by weight of water, wherein eachweight is relative to the total weight of the cohesive, elastic dough;forming the cohesive, elastic dough into a shaped article; and dryingthe shaped article in an environment having a temperature less thanabout 25° C.
 2. A solid biodegradable article selected from the groupconsisting of food storage containers, food utensils, beveragecontainers, boxes, toys and filters prepared by forming a cohesive,elastic dough consisting essentially of hydrated wheat gluten preparedby mixing at a temperature less than about 60° C. from about 0.1 toabout 0.9 parts by weight of a commercial wheat gluten purified byprotein fractionation or extraction with from about 0.9 to about 0.1parts by weight of water, wherein each weight is relative to the totalweight of the cohesive, elastic dough; forming the cohesive, elasticdough into a shaped article; and placing the shaped article in anenvironment sufficient to remove excess water from the shaped article.